A saturated carboxylic acid, such as propionic acid (PA), can be catalytically reacted with formaldehyde (FA), in the vapor phase, to produce an alpha, beta-ethylenically unsaturated carboxylic acid, such as methacrylic acid (MA), and water. Catalysts to effect such reactions are well known in the art. See, e.g., U.S. Pat. No. 3,247,248 to Sims et al. Such catalysts typically comprise a catalyst support and a catalytically-active ingredient on the support. The produced unsaturated carboxylic acid can be esterified to a commercially useful unsaturated carboxylic acid ester, such as methyl methacrylate (MMA).
MMA is a widely-used monomer. Illustrative of the many products that can be made from MMA-derived polymers are advertising displays, lighting fixtures, glazing materials, structural panels, and the like, molding resins for automobile tail-light lenses, plumbing fixtures, and the like, as well as constituents of a variety of surface coatings, adhesives, inks, floor polishes, and the like.
Many of the vapor-phase MA-synthesis catalysts that are commercially available tend to deactivate with use over time and accordingly must either be regenerated or replaced. In some instances, the catalyst support is depleted of its catalytically-active ingredient, and this depletion results in the catalyst being progressively less active over time. In a commercial production environment, a deactivated catalyst is typically replaced with fresh catalyst when its performance drops below a desired catalyst activity, conversion or selectivity value.
It can be appreciated that the replacement of the deactivated catalyst may involve unscheduled process downtime, which is undesirable and can be costly. Other systems for regenerating or replacing deactivated catalyst can involve investment in auxiliary processing equipment, which also can be costly. The present invention not only provides a method for extending useful life of the catalyst but also provides a method for replenishing the catalytically-active ingredient of a catalyst as well.